KR102273762B1 - VoLTE SYSTEM, CONTROL METHOD THEREOF, PGW AND CSCF COMPRISED IN THE SYSTEM, CONTROL METHOD THEREOF - Google Patents

Abstract

The present invention relates to a Voice over Long Term Evolution (VoLTE) system and a method for controlling the same, and to a PDN Gateway (PGW) and a Call Session Control Function (CSCF) included in the system and a method for controlling the same. A method of controlling a Voice over Long Term Evolution (VoLTE) system including a Mobility Management Entity (MME), a Home Subscriber Server (HSS), a PDN Gateway (PGW), and a Call Session Control Function (CSCF) according to the present invention, when the PGW receives the incoming packet from the CSCF, determining whether called party information corresponding to the incoming packet exists; transmitting, by the PGW, a called party information absence notification signal to the CSCF that has transmitted the incoming packet when the called party information does not exist as a result of the determination in the step; transmitting, by the CSCF, a subscriber session deletion notification signal to the HSS when receiving an incoming call information absence notification signal from the PGW; transmitting, by the HSS, a subscriber location information deletion request message to the MME when a subscriber session deletion notification signal is received from the CSCF; and transmitting, by the MME, a reconnection control signal to a corresponding called terminal when receiving the subscriber location information deletion request message from the HSS.

Description

VoLTE (Voice over Long Term Evolution) system and its control method, PGW (PDN Gateway) and CSCF (Call Session Control Function) included in the system and its control method {VoLTE SYSTEM, CONTROL METHOD THEREOF, PGW AND CSCF COMPRISED IN THE SYSTEM, CONTROL METHOD THEREOF}

The present invention relates to a Voice over Long Term Evolution (VoLTE) system and a control method thereof, and a PDN Gateway (PGW) and a Call Session Control Function (CSCF) included in the system and a control method thereof, and more particularly, to the PGW The present invention relates to a VoLTE system and a control method thereof for quickly recovering subscriber information in a PGW so that an incoming call is normally connected when subscriber information does not exist, and a PGW and CSCF included in the system.

The PDN Gateway (PGW), a component of the Voice over Long Term Evolution (VoLTE) system, stores and manages subscriber information for session connection or maintenance. In some cases, such subscriber information is deleted from the PGW due to equipment failure, etc. may occur.

Conventionally, when there is no subscriber information in the PGW, when a communication terminal attempts to send, a reattach procedure is performed to restore the subscriber information to the PGW, but there is a problem in that the subscriber information is not restored when an incoming call occurs.

That is, when an incoming packet is received from the PGW in a state where subscriber information does not exist in the PGW, the PGW discards the incoming packet as it is. The problem arises that it cannot be received.

Patent Publication No. 10-2013-0006284

The present invention has been devised to solve the above problems of the prior art, and its purpose is to provide a subscriber in the PGW at the point in time when an incoming call occurs to the corresponding communication terminal even if the predetermined communication terminal does not attempt to send the subscriber information when the subscriber information is deleted in the PGW. It is to provide a VoLTE system and a control method therefor, and a PGW and CSCF included in the system, and a control method therefor, for recovering information.

VoLTE (Voice over Long Term Evolution) including a Mobility Management Entity (MME), a Home Subscriber Server (HSS), a PDN Gateway (PGW), and a Call Session Control Function (CSCF) according to the present invention in order to achieve the above object The control method of the system includes: when the PGW receives an incoming packet from the CSCF, determining whether there is called party information corresponding to the incoming packet; transmitting, by the PGW, a called party information absence notification signal to the CSCF that has transmitted the incoming packet when the called party information does not exist as a result of the determination in the step; transmitting, by the CSCF, a subscriber session deletion notification signal to the HSS when receiving an incoming call information absence notification signal from the PGW; transmitting, by the HSS, a subscriber location information deletion request message to the MME when a subscriber session deletion notification signal is received from the CSCF; and transmitting a reconnection control signal to the corresponding called terminal when the MME receives the subscriber location information deletion request message from the HSS.

In addition, in order to achieve the above object, a control method of a PDN Gateway (PGW) that is included in a Voice over Long Term Evolution (VoLTE) system according to the present invention and communicates with a Call Session Control Function (CSCF) is, when receiving a packet, determining whether called party information corresponding to the incoming packet exists; and transmitting a callee information absence notification signal to the CSCF that transmitted the incoming packet when the called party information does not exist as a result of the determination in the step.

In addition, in order to achieve the above object, it is included in the VoLTE (Voice over Long Term Evolution) system according to the present invention and communicates with a Home Subscriber Server (HSS) and a PDN Gateway (PGW). Control of a CSCF (Call Session Control Function) The method comprises: sending an incoming packet to the PGW; and transmitting, to the HSS, a subscriber session deletion notification signal for inducing reconnection of a called terminal corresponding to the corresponding incoming packet when a called party information absence notification signal is received from the PGW that transmitted the incoming packet.

In addition, in order to achieve the above object, the VoLTE system according to the present invention includes a Mobility Management Entity (MME), a Home Subscriber Server (HSS), a PDN Gateway (PGW), and a Call Session Control Function (CSCF). When the PGW receives the incoming packet from the CSCF, it determines whether the called party information corresponding to the incoming packet exists or not, and if the called party information does not exist as a result of the determination, the PGW sends a called party information absence notification signal to the CSCF that transmitted the incoming packet. After transmitting the incoming packet to the PGW, the CSCF transmits a subscriber session deletion notification signal to the HSS when receiving an incoming information absence notification signal from the corresponding PGW, and the HSS sends a subscriber session deletion notification from the CSCF When the signal is received, it transmits a subscriber location information deletion request message to the MME, and when the MME receives the subscriber location information deletion request message from the HSS, it transmits a reconnection control signal to the corresponding called terminal.

In addition, in order to achieve the above object, a PDN Gateway (PGW) included in a Voice over Long Term Evolution (VoLTE) system according to the present invention and communicating with a Call Session Control Function (CSCF) receives an incoming packet from the CSCF. a receiving unit; a judging unit for determining whether or not the called party information corresponding to the incoming packet received by the receiving unit exists; and a transmitter for transmitting a callee information absence notification signal to the CSCF that has transmitted the incoming packet when the callee information does not exist as a result of the determination of the determination unit.

In addition, in order to achieve the above object, the CSCF (Call Session Control Function) that is included in the Voice over Long Term Evolution (VoLTE) system according to the present invention and communicates with the Home Subscriber Server (HSS) and the PDN Gateway (PGW) is, a receiver for receiving a callee information absence notification signal from the PGW; Sends an incoming packet to the PGW, and when an incoming information absence notification signal is received from the PGW as a response to the incoming packet, a subscriber session deletion notification signal for inducing reconnection of the called terminal corresponding to the incoming packet and a transmitter for transmitting to the HSS.

As described above, according to the present invention, when the called party information is deleted from the PGW, the called party information corresponding to the corresponding called party can be newly registered in the PGW by the operations of the PGW and the CSCF at the time when an incoming signal to the corresponding called party is received. have.

Accordingly, the problem that an incoming call is not received to a called party whose called party information is deleted in the PGW can be solved early.

1 is a schematic configuration diagram of a VoLTE system according to an embodiment of the present invention;
Figure 2 is a functional block diagram of the PGW of Figure 1;
3 is a functional block diagram of the CSCF of FIG. 1;
4 is a control flowchart of a VoLTE system according to an embodiment of the present invention;
5 is a control flow diagram of a PGW according to an embodiment of the present invention;
6 is a control flowchart of a CSCF according to an embodiment of the present invention.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

Hereinafter, each embodiment according to the present invention is merely an example for helping understanding of the present invention, and the present invention is not limited to these embodiments. In particular, the present invention may be composed of a combination of at least any one of individual components, individual functions, or individual steps included in each embodiment.

A schematic configuration of a Voice over Long Term Evolution (VoLTE) system according to an embodiment of the present invention is shown in FIG. 1 .

FIG. 1 shows the configuration of a VoLTE system connected to the called terminal for convenience, and the configuration connected to the calling terminal is omitted.

The VoLTE system may be divided into a Long Term Evolution (LTE) part and an IP Multimedia Subsystem (IMS) part. In this case, the CSCF 200 of FIG. 1 may belong to the IMS part, but these components are components for VoLTE communication as a whole. Therefore, in this embodiment, each component will be described as belonging to the VoLTE system without distinction of individual systems or networks.

The VoLTE system according to an embodiment of the present invention transmits and receives Voice over IP (VoIP) packets via an LTE network to enable mutual communication, and as shown in FIG. 1, an Evolved Node B (eNB) 600 , Mobility Management Entity (MME) (400), Home Subscriber Server (HSS) (300), Serving Gateway (SGW) (500), PDN Gateway (PGW) (100), and Call Session Control Function (CSCF) (200) It may be composed of

The functions defined in the international standards of these components are briefly described as follows.

First, the eNB 600 may be referred to as an 'LTE base station'. It is a device that provides a wireless connection between a user equipment (UE) 700 and an LTE network, and in FIG. 1 , between the UE 700 and the eNB 600 is It is preferable that the wireless connection is configured as a wired connection for the rest.

Here, the UE 700 refers to a user terminal, and may be a terminal having a call function, such as a smartphone, or a USB dongle (USB type, connected to a laptop to use wireless Internet) for the purpose of data communication only. have.

The MME 400 is a device that serves as the brain of the LTE network and authenticates the UE 700. At this time, the MME 400 receives the key information for authenticating the UE 700 from the HSS 300 and performs the UE 700 authentication. do. And the MME 400 manages the EPS bearer, where the EPS bearer is logically created in the {UE 700 - eNB 600 - S-GW - P-GW} section for the UE 700 to use the Internet. It can be called an in-tunnel (GTP tunnel), and the MME 400 is a device involved in the creation/change/release of the tunnel.

Furthermore, the MME 400 manages the mobility status of the subscriber, in particular, whether the current UE 700 is attached to the network, not attached, and whether or not using the Internet while attached or not (Idle state). .

The HSS 300 serves as a central database of the LTE network having key information for authentication and a subscriber profile for each UE 700 (subscriber), and the subscriber profile includes a QoS class suitable for the service product subscribed to by each subscriber. Information (priority, maximum available bandwidth, etc.) is included, and key information and subscriber profile for authentication are transmitted to the MME 400 as described above when the UE 700 accesses the LTE network.

The SGW 500 serves as an anchoring role during handover between the eNBs 600 , for example, in a handover situation of the UE 700 (the UE 700 that was initially attached to the eNB 600 1 and used the Internet). ) moves to release the connection with the eNB (600)1 and connects to the eNB (600)2) to perform an anchoring role.

The PGW 100 allocates an IP address to the terminal, performs anchoring for the SGWs 500 in a handover situation, and applies different QoS policies for each UE 700 (activities such as priority and bandwidth control) ) and performs a function of managing Accounting Data for each UE (700).

In addition, the CSCF 200 is a device that performs SIP-based call control and session handling functions, and enables various multimedia services to be provided.

The CSCF 200 may be divided into various parts in terms of its logical function. For example, it may be divided into P-CSCF (Proxy-CSCF), I-CSCF (Interrogating-CSCF), and S-CSCF (Serving-CSCF). have.

Here, the P-CSCF is a contact point with the UE 700 in the IMS Network, which proxying the SIP message, and provides functions such as security and compression with the UE 700, and the I-CSCF operates as a contact point of the IMS Network of the network operator. and performs the role of routing SIP messages to other nodes within the IMS network.

And the S-CSCF manages the session state for the SIP Message, executes call control to provide the service requested by the Subscriber through routing to the AS, and acts as a SIP Registrar to process the registration request from the UE (700), It performs the function of managing the state.

Hereinafter, each component will be described focusing on functions indicating features of the present invention other than functions defined in the 3rd Generation Partnership Project (3GPP) standard described above.

First, the PGW 100 may receive an incoming packet from the CSCF 200 , where the incoming packet means a packet to be transmitted to a predetermined called party (eg, called party's terminal).

The PGW 100 determines the presence or absence of the called party information corresponding to the incoming packet, and if the called party information does not exist as a result of the determination, the PGW 100 transmits a callee information absence notification signal to the CSCF 200 that has transmitted the incoming packet. carry out

That is, the conventional PGW 100 discards the corresponding packet when there is no called party information corresponding to the incoming packet, but the PGW 100 according to an embodiment of the present invention transmits the called party information absence notification signal to the CSCF 200 ) is sent to

To this end, the PGW 100 may be configured to include a receiving unit 110 , a determining unit 120 , a transmitting unit 130 , and a storage unit 140 as shown in FIG. 2 .

Here, the storage unit 140 stores information about each subscriber for packet processing.

The receiving unit 110 performs a function of receiving an incoming packet from the CSCF 200, and the determining unit 120 stores the called party information corresponding to the incoming packet received by the receiving unit 110 in the storage unit 140. determine whether there is That is, the determination unit 120 determines whether the called party information exists. Determining the presence or absence of the called party information corresponding to the incoming packet corresponds to a known technique, and thus a more detailed description thereof will be omitted.

The transmitter 130 performs a function of transmitting a callee information absence notification signal to the CSCF 200 that has transmitted the incoming packet when the callee information does not exist as a result of the determination of the determination unit 120 .

Here, when the callee information does not exist as a result of the determination of the determination unit 120 , the transmitter 130 does not have the callee information only when the incoming packet received from the CSCF 200 is an INVITE packet according to the Session Initiation Protocol (SIP). A notification signal may be transmitted to the CSCF 200 . That is, in the case where the incoming packet is a packet other than the INVITE packet, if the called party information does not exist, the packet is discarded as it is.

Here, the subscriber session deletion notification signal transmitted to the CSCF 200 may be an Internet Control Message Protocol (ICMP) Destination Unreachable packet. That is, the transmission unit 130 transmits a type 3 “target unreachable” packet of the Internet Control Message Protocol (ICMP) to the CSCF 200 .

On the other hand, the CSCF 200 transmits the incoming packet received from the sender to the PGW 100 and then, when an incoming information absence notification signal is received from the corresponding PGW 100, a subscriber session deletion notification signal to the HSS 300. It performs the function of sending.

To this end, the CSCF 200 may be configured to include a receiving unit 210 and a transmitting unit 220 as shown in FIG. 3 , wherein the receiving unit 210 receives an incoming packet from the sender to the called party. Of course, it performs a function of receiving a callee information absence notification signal from the PGW 100,

The transmitter 220 transmits an incoming packet received from the sender to the PGW 100 as well as a function of transmitting an incoming packet received from the PGW 100 as a response to the incoming packet. It performs a function of transmitting a subscriber session deletion notification signal for inducing reconnection of the called terminal corresponding to the corresponding incoming packet to the HSS 300 .

Here, the callee information absence notification signal received from the PGW 100 may be an Internet Control Message Protocol (ICMP) Destination Unreachable packet as described above, and the subscriber session deletion notification signal transmitted to the HSS 300 is ASR (Abort-Session). -Request) message.

On the other hand, the HSS 300 performs a function of transmitting a subscriber location information deletion request message to the MME 400 when a subscriber session deletion notification signal is received from the CSCF 200 , and the MME 400 transmits a subscriber location information deletion request message from the HSS 300 . When a location information deletion request message is received, a function of transmitting a reconnection control signal to a corresponding called terminal is performed.

Accordingly, the called terminal performs a reconnection processing process. Since the reconnection processing process performed by a predetermined terminal according to the reconnection control signal of the MME 400 is only a known technique, a more detailed description will be omitted.

As described above, when an incoming call to the corresponding called terminal is received when the called party information is deleted in the PGW 100, the PGW 100 transmits a kind of request signal to the CSCF 200, so that the corresponding called terminal eventually reconnects. and to restore the incoming information to the PGW 100 so that the called terminal can make a call.

Hereinafter, the overall control flow of the VoLTE system according to an embodiment of the present invention will be described with reference to FIG. 4 .

In FIG. 4 , since the eNB 600 and the SGW 500 merely perform a known technique, the illustration thereof is omitted.

It is assumed that subscriber information currently exists in the terminal, the MME 400 , the HSS 300 , and the CSCF 200 , but the subscriber information is deleted in the PGW 100 due to a device malfunction or the like.

In this state, when the CSCF 200 transmits an incoming signal, that is, an INVITE message received from the calling party, to the PGW 100 (step S1), the PGW 100 checks whether there is recipient information corresponding to the INVITE message. In this embodiment, it is assumed that the called party information does not exist in the PGW 100, so the PGW 100 transmits a Destination Unreachable packet corresponding to ICMP type 3 to the CSCF 200 (step S3).

Upon receiving the above-described ICMP packet from the PGW 100, the CSCF 200 transmits an Abort Session Request (Cause: Timeout De-reg) signal corresponding to the subscriber session deletion notification signal to the HSS 300 (step S5).

Upon receiving the above-described Abort Session Request from the CSCF 200, the HSS 300 transmits an Abort Session Answer signal that is the response to the CSCF 200 (step S7), and requests the MME 400 to delete subscriber location information. A Cancel Location Request (Subscription withdrawal) signal corresponding to the message is transmitted (step S9).

Upon receiving the Cancel Location Request from the HSS 300, the MME 400 transmits a Detach Request (Reattach required) signal corresponding to a reconnection control signal to the corresponding called terminal (step S23).

Steps S11 to S21 in FIG. 1 correspond to known general processing procedures, and thus a more detailed description thereof will be omitted.

Upon receiving the above-described Detach Request from the MME 400, the called terminal newly performs Attach (step S27), and then performs SIP REGISTER (step S29).

In this way, the called party information corresponding to the called party is registered in the PGW 100 through the reconnection process of the called terminal, so that an incoming call can reach the corresponding called terminal.

Here, the PGW 100 in which the called party information corresponding to the called terminal is registered may correspond to the PGW 100 in which the corresponding called party information was previously registered, or may correspond to another PGW (not shown).

Hereinafter, a control process of the PGW 100 according to an embodiment of the present invention will be described with reference to FIG. 5 .

When an incoming packet is received from the CSCF 200 (step S31), the PGW 100 analyzes the received incoming packet (step S33), and determines whether called party information corresponding to the incoming packet exists (step S35) ).

If it is determined that the called party information exists, the PGW 100 transmits the corresponding packet to the called party (for example, the called terminal via the SGW 500) to communicate (step S37), and as a result of the determination, the called party information is If it does not exist, the PGW 100 discards the incoming packet (step S41) if the incoming packet is not an INVITE message (step S39), whereas, if the incoming packet is an INVITE message (step S39), the ICMP packet generated (step S43) and transmitted to the CSCF 200 (step S45).

6 is a control process of the CSCF 200 according to an embodiment of the present invention.

The CSCF 200 transmits the incoming INVITE message received from the calling party to the PGW 100 (step S51), and waits whether a 180 Ringing signal is received (step S53).

If the 180 Ringing signal is received from the PGW 100 (step S55), the CSCF 200 performs normal call processing according to a known method (step S57), and if an ICMP Destination Unreachable packet is received from the PGW 100 (step S55) When it is (step S59), the CSCF 200 transmits an ASR (Timeout De-reg) signal to the HSS 300 (step S61).

Meanwhile, it goes without saying that the process of performing each of the above-described embodiments may be performed by a program or application stored in a predetermined recording medium (eg, computer-readable). Here, the recording medium includes an electronic recording medium such as a random access memory (RAM), a magnetic recording medium such as a hard disk, and an optical recording medium such as a compact disk (CD).

In this case, the program stored in the recording medium may be executed on hardware such as a computer or a smart phone to perform each of the above-described embodiments. In particular, at least one of the functional blocks of the PGW and the CSCF according to the present invention described above may be implemented by such a program or an application.

In addition, the present invention is not limited to the specific embodiments described above, but can be practiced with various modifications and modifications within the scope without departing from the gist of the present invention. It will be apparent that such modifications and variations are included in the present invention provided they fall within the scope of the appended claims.

100: PGW 200: CSCF
300: HSS 400: MME
500: SGW 600: eNB
700: UE 110: receiver
120: judgment unit 130: transmission unit
140: storage 210: receiver
220: transmission unit

Claims (16)

In the control method of a VoLTE (Voice over Long Term Evolution) system including a Mobility Management Entity (MME), a Home Subscriber Server (HSS), a PDN Gateway (PGW), and a Call Session Control Function (CSCF),
(a) when the PGW receives an incoming packet from the CSCF, determining whether called party information corresponding to the incoming packet exists;
(b) transmitting, by the PGW, a callee information absence notification signal to the CSCF that transmitted the incoming packet when the called party information does not exist as a result of the determination in step (a);
(c) when the CSCF receives an incoming information absence notification signal from the PGW, transmitting a subscriber session deletion notification signal to the HSS;
(d) transmitting, by the HSS, a subscriber location information deletion request message to the MME when a subscriber session deletion notification signal is received from the CSCF;
(e) when the MME receives the subscriber location information deletion request message from the HSS, transmitting a reconnection control signal to the corresponding called terminal. According to claim 1,
In step (b), when the incoming packet received from the CSCF is an INVITE packet according to SIP (Session Initiation Protocol), the PGW generates an Internet Control Message Protocol (ICMP) Destination Unreachable packet as the callee information absence notification signal. to transmit to the CSCF, and if the incoming packet received from the CSCF is not an INVITE packet according to SIP (Session Initiation Protocol), the corresponding incoming packet is discarded. According to claim 1,
The method of controlling a VoLTE system, characterized in that the subscriber session deletion notification signal transmitted by the CSCF to the HSS in step (c) is an Abort-Session-Request (ASR) message. In the control method of a PDN Gateway (PGW) included in a Voice over Long Term Evolution (VoLTE) system and communicating with a Call Session Control Function (CSCF),
(a) when receiving an incoming packet from the CSCF, determining whether or not there is called party information corresponding to the incoming packet;
(b) when the called party information does not exist as a result of the determination in step (a), transmitting a called party information absence notification signal to the CSCF that transmitted the incoming packet. 5. The method of claim 4,
In step (b), when the incoming packet received from the CSCF is an INVITE packet according to the SIP (Session Initiation Protocol), an Internet Control Message Protocol (ICMP) Destination Unreachable packet is generated as the called party information absence notification signal, and the CSCF and, if the incoming packet received from the CSCF is not an INVITE packet according to SIP (Session Initiation Protocol), the corresponding incoming packet is discarded. In a method of controlling a Call Session Control Function (CSCF) included in a Voice over Long Term Evolution (VoLTE) system and communicating with a Home Subscriber Server (HSS) and a PDN Gateway (PGW),
(a) sending an incoming packet to the PGW;
(b) when a callee information absence notification signal is received from the PGW that transmitted the incoming packet, transmitting a subscriber session deletion notification signal for inducing reconnection of the called terminal corresponding to the corresponding incoming packet to the HSS; CSCF control method. 7. The method of claim 6,
The callee information absence notification signal received from the PGW is an Internet Control Message Protocol (ICMP) Destination Unreachable packet, and the subscriber session deletion notification signal transmitted to the HSS is an Abort-Session-Request (ASR) message. control method. A computer-readable recording medium recording a program for executing the method of any one of claims 1 to 7. 8. An application stored on a medium in combination with hardware to execute the method of any one of claims 1 to 7. Including a Mobility Management Entity (MME), a Home Subscriber Server (HSS), a PDN Gateway (PGW), and a Call Session Control Function (CSCF),
When the PGW receives the incoming packet from the CSCF, it determines whether the called party information corresponding to the incoming packet exists or not, and if the called party information does not exist as a result of the determination, a callee information absence notification signal to the CSCF that transmitted the incoming packet to send,
After transmitting the incoming packet to the PGW, the CSCF transmits a subscriber session deletion notification signal to the HSS when receiving an incoming information absence notification signal from the corresponding PGW;
When the HSS receives a subscriber session deletion notification signal from the CSCF, the HSS transmits a subscriber location information deletion request message to the MME,
VoLTE system, characterized in that the MME transmits a reconnection control signal to the corresponding called terminal upon receiving the subscriber location information deletion request message from the HSS. 11. The method of claim 10,
When the called party information does not exist, if the incoming packet received from the CSCF is an INVITE packet according to the SIP (Session Initiation Protocol), the PGW generates an Internet Control Message Protocol (ICMP) Destination Unreachable packet as the called party information absence notification signal and generates the A VoLTE system, wherein the incoming packet is transmitted to the CSCF and discarded if the incoming packet received from the CSCF is not an INVITE packet according to SIP (Session Initiation Protocol). 11. The method of claim 10,
The subscriber session deletion notification signal transmitted by the CSCF to the HSS is an Abort-Session-Request (ASR) message. In a PDN Gateway (PGW) included in a Voice over Long Term Evolution (VoLTE) system and communicating with a Call Session Control Function (CSCF),
a receiver for receiving an incoming packet from the CSCF;
a judging unit for determining whether or not there is called party information corresponding to the incoming packet received by the receiving unit;
and a transmitter for transmitting a callee information absence notification signal to the CSCF that has transmitted the incoming packet when the called party information does not exist as a result of the determination of the determining unit. 14. The method of claim 13,
If the incoming packet received from the CSCF is an INVITE packet according to the SIP (Session Initiation Protocol) when the determination unit determines that the called party information does not exist, as the called party information absence notification signal, the ICMP (Internet Control Message Protocol) Destination Unreachable A PGW, wherein a packet is generated and transmitted to the CSCF, and if the incoming packet received from the CSCF is not an INVITE packet according to SIP (Session Initiation Protocol), the corresponding incoming packet is discarded. In a CSCF (Call Session Control Function) included in a Voice over Long Term Evolution (VoLTE) system and communicating with a Home Subscriber Server (HSS) and a PDN Gateway (PGW),
a receiver for receiving a callee information absence notification signal from the PGW;
Sends an incoming packet to the PGW, and when an incoming information absence notification signal is received from the PGW as a response to the incoming packet, a subscriber session deletion notification signal for inducing reconnection of the called terminal corresponding to the incoming packet CSCF comprising a transmitter for transmitting to the HSS. 16. The method of claim 15,
CSCF, characterized in that the called party information absence notification signal received from the PGW is an Internet Control Message Protocol (ICMP) Destination Unreachable packet, and the subscriber session deletion notification signal transmitted to the HSS is an Abort-Session-Request (ASR) message.

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